Because a laser pulse has the features of good direction and anti-jamming, the laser pulse imaging technique is widely used to measure the three-dimensional information of the ground. The laser echo acquiring and processing technique is a key technique in laser pulse imaging. Through the analysis of laser echoes, the information on roughness, gradient and reflection of the ground can be acquired. In this paper, various lidar systems are analysed. The laser echo acquiring techniques which have been used are reviewed. The prospective development of the technique is described to some extent.